Understanding Custom GIF Playback

Unlike simply embedding a GIF with an tag, building a custom player involves reading the GIF file's data, extracting individual frames and their delays, and then rendering these frames sequentially onto an HTML Canvas or using other rendering techniques.

Core Concepts

• GIF Parsing: Reading the binary data of a GIF file to understand its structure, global color table, and individual frame information (image data, local color table, disposal method, delay time).
• Frame Rendering: Drawing each frame onto an HTML Canvas element at the correct timing based on the frame delays.
• Playback Control: Implementing JavaScript functions to manage the animation loop, pause/play, seek to specific frames, and control speed.

Basic Structure (Conceptual)

Here's a simplified conceptual outline of the JavaScript logic:

// Assuming you have a way to load and parse the GIF data
// and extract frames and delays into an array

let frames = []; // Array of image data for each frame
let delays = []; // Array of delay times for each frame
let currentFrameIndex = 0;
let animationInterval = null;
const canvas = document.getElementById('gifCanvas');
const ctx = canvas.getContext('2d');

function renderFrame(index) {
  // Draw the image data of the frame at 'index' onto the canvas
  // Handle disposal methods from previous frame
}

function playAnimation() {
  if (animationInterval) clearInterval(animationInterval);

  animationInterval = setInterval(() => {
    renderFrame(currentFrameIndex);
    currentFrameIndex = (currentFrameIndex + 1) % frames.length;
  }, delays[currentFrameIndex]); // Use the delay for the *current* frame
}

function pauseAnimation() {
  clearInterval(animationInterval);
  animationInterval = null;
}

function stopAnimation() {
  pauseAnimation();
  currentFrameIndex = 0;
  renderFrame(currentFrameIndex); // Show the first frame
}

// Add event listeners to buttons (playBtn, pauseBtn, stopBtn, etc.)
// Call playAnimation(), pauseAnimation(), stopAnimation() accordingly

Note: This is a highly simplified example. A real custom GIF player requires robust GIF parsing logic and careful handling of various GIF specifications (like disposal methods).

Libraries for Assistance

Building a GIF parser from scratch is complex. Consider using existing JavaScript libraries designed for this purpose, such as gifuct-js or others available on npm.